Compressor geometry control apparatus for gas turbine engine

ABSTRACT

A fluid pressure responsive actuator responsive to first and second air pressures, at least one of which is compressor generated and varies as a function of engine speed, and connected to actuate compressor geometry varying means such as compressor pressurized air bleed means or compressor air inlet &#39;&#39;&#39;&#39;flow fence or restriction&#39;&#39;&#39;&#39; means thereby varying mass air flow through one or more of the compressor stages to avoid characteristic unstable operation of the compressor during an engine acceleration. A compressor bleed valve may be actuated to an open position in response to a predetermined ratio of the first and second air pressures during an engine acceleration to a selected speed and closed in proportion to a decreasing ratio of the first and second air pressures as the engine approaches the selected value. A compressor air inlet &#39;&#39;&#39;&#39;flow fence or restriction&#39;&#39;&#39;&#39; may be held in a closed position until a predetermined ratio of the first and second air pressures is reached and subsequently opened in proportion to an increasing ratio of the first and second air pressures to cause an increase in effective flow area of the compressor air inlet during an acceleration of the engine to a selected speed.

1 States tet 1 1 1111 3, Eastman et a1. [4 N01 19, 11974 1 COMPRESSORGEOMETRY CONTROL APPARATUS FOR GAS TURBINE ENGINE [57] AESTHMQT [75]Inventors: James M. Eastman; Robert W.

Schuster, both of South Bend A fluid pressure responsive actuatorresponsive to first and second air pressures, at least one of which iscom- 1 Assigneei The Bendix 'p t South pressor generated and varies as afunction of engine Bend, speed, and connected to actuate compressorgeometry [22] Filed: Apt 29 1973 varying means such as compressorpressurized air bleed means or compressor air inlet flow fence or re- PP-I 34 ,251 striction means thereby varying mass air flow through one ormore of the compressor stages to avoid 52] us. on 415/30, 415/17,60/3929 Characteristic unstable operam" of the Compressor [51] um CH HW2C WM Fold 17/06 Fold 19/00 during an engine acceleration. A compressorbleed [58] Field Search "4/5/17, 30 1 1 60/3929 valve may be actuated toan open position in response to a predetermined ratio of the first andsecond air [56] References Cited pressures during an engine accelerationto a selected speed and closed in proportion to a decreasing ratio ofUNITED STATES PATENTS the first and second air pressures as the engineap- Lundqulst proaches the elected value A compressor air inlet flowfence or restriction" may be held in a closed position until apredetermined ratio of the first and second air pressures is reached andsubsequently opened 3,526,091 9/1970 Schuster 60/391611 in Proportion toan increasing ratio of the first and second air pressures to cause anincrease in effective Primary Examine, wi||iam L Freeh flow area of thecompressor air inlet during an accel- Assismm casaregola eration of theengine to a selected speed. Art ,A r, F' G d H.Ch g z 221 35 [rm or onenez 12 Claims, 7 Drawing 1F igures R we I34 1 20 Ma Pa L1? 142 PA 732146 l I PA I26 206 [5' l6! 1 i I l9 OPEN CLOSED L ie COMPRESSOR GEOMETRYCONTROL APPARATUS FOR GAS TURBINE ENGINE BACKGROUND OF THE INVENTION Ina high performance axial flow compressor gas turbine engine, it is oftennecessary to control the mass air flow through the compressor to avoidcharacteristic unstable operation of the compressor particularly duringan engine acceleration. Such control may be exercised by either of twoconventional ways as, for example, by bleeding or venting compressorstages to a suitable relatively lower pressure drain source or byvarying the effective flow area of the compressor inlet to increase ordecrease the mass air flow to the compressor. It will be recognized thatsuch bleeding of pressurized air or restriction of air flow to thecompressor has an undesirable effect on the efficiency and power of theengine and therefore should be limited to a minimum during engineoperation.

Various prior air compressor geometry varying means are known as, forexample, that shown and described in U.S. Pat. No. 3,172,259 issued Mar.9, 1965 to Howard L. North, Jr. and U.S. Pat. No. 3,646,753 issued Mar.7, 1972 to Michael E. Coleman et al. The prior art actuators of which weare aware are adapted to actuate one or more bleed valves to a fullyopen or closed position in response to selected engine operatingparameters which does not provide the variable degree of control overthe bleed air flow from the compressor that applicants actuatorprovides. It will be recognized that abrupt opening or closing of acompressor bleed valve or inlet flow fence" may have an undesirableeffect on compressor operation thereby rendering applicants actuatoradvantageous in that gradual opening or closing of a bleed valve isestablished.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a gas turbine engine compressor geometry varying actuatorresponsive to a fluid pressure ratio which varies as a function ofengine speed and adapted to control the degree of actuation inproportion to engine speed.

It is another object of the present invention to provide a gas turbineengine compressor bleed valve actuator which controls opening of a bleedvalve in proportion to engine speed.

It is an additional object of the present invention to provide a gasturbine engine compressor inlet flow fence actuator which is responsiveto a ratio of air pressures at least one of which pressures is acompressor generated air pressure variable as a function off enginespeed.

Other objects and advantages of the present invention will be apparentfrom the following description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof a gas turbine engine and compressor bleed valve system thereforembodying the present invention;

FIG. 2 is a schematic view in section of the present invention shownremoved from the control system of FIG. 1;

FIG. 3 is a section view taken on line 3-3 of FIG. 2;

FIG. 4 is a curve or plot showing bleed valve position vs. pressureratio Py/Pc;

FIG. 5 is a curve or plot showing the relationship between pressureratio Py/Pg and engine speed N.

FIG. 6 represents the structure of FIG. 2 modified for use incontrolling a compressor inlet flow fence."

FIG. 7 is a curve or plot showing flow fence position vs. pressure ratioP /P DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, inparticular, numeral 20 designates a conventional gas turbine engineprovided with an air inlet 22 upstream from a multiple stage axial flowcompressor 24 which discharges pressurized air flow to one or morecombustion chambers 26. Hot motive gas generated in the combustionchamber 26 and discharged therefrom is passed through a gas turbine 28connected to drive the compressor 24 via a shaft 29. The discharge gasfrom the gas turbine 28 is expelled through a discharge nozzle 30thereby providing a propelling thrust.

A controlled rate of fuel flow is supplied to combustion chamber 26 viaa fuel injection nozzle 32 supplied pressurized fuel by a fuel manifold34 connected thereto and provided with a fuel supply conduit 36 leadingfrom the outlet of a fuel control generally indicated by 38. The fuelcontrol 38 is adapted to receive control input signals including enginerotational speed, N, via suitable gear and shafting 40, power requestvia a throttle lever 42 and compressor pressurized air at pressuree Pvia a conduit 44 providing fluid communication between control 38 andthe discharge section of compressor 24.

One or more conventional compressor air bleed valves 46 suitablyconnected to a selected stage or stages of the compressor 24 and adaptedto vent compressor pressurized air therefrom to a suitable relativelylow pressure drain source such as the atmosphere, P is actuated by alinkage generally indicated by 48 and connected to bleed valve actuator50.

The fuel control 38 is conventional and may be of any suitable type suchas that shown and described in U.S. Pat. No. 3,526,091 issued to R. W.Schuster and having the same assignee as the present application. Aportion of the control 38 is broken away to show the operatingrelationship between it and the bleed valve actuator 50. Reference ismade to U.S. Pat. No. 3,526,091 for additional details of structure andoperation of fuel control 38.

The fuel control 38 includes a casing 52 having an outlet 54 connectedto conduit 36 and an inlet 56 connected to a source of pressurized! fuelwhich may include a fuel tank and engine driven fuel pump, not shown.

Fuel passes from inlet 56 to outlet 54 via conduit means includingpassage 58, a variable area fuel metering orifice 60, passage 62 andfuel cut-off valve 64. Fuel bypass valve means generally indicated by 66responsive to the fuel pressure differential across orifice 60 divertsfuel at unmetered fuel pressure P to a fuel bypass outlet 68 whichcommunicates with the inlet of the fuel pump, not shown,, to therebymaintain the pressure differential across orifice 60 at a predeterminedconstant value regardless of the effective flow area of orifice 60. Afuel metering valve 70 suitably connected to orifice 60 and movablerelative thereto to vary the flow area of the same controls the rate offuel flow therethrough.

The valve 70 is actuated by a linkage mechanism generally indicated by72 which responds to a governor bellows 74 and a relatively smallerevacuated acceleration bellows 76 rigidly linked together by a stem 78.The bellows 74 is responsive to air pressures Py and P and evacuatedbellows 76 is responsive to pressure P which pressures Py and P Xderived from air at compressor discharge pressure P A conduit 80containing a fixed area restriction 82- communicates conduit 44 atcompressor discharge air pressure P with a relatively low pressure drainsource P The effective flow area of the discharge end of passage 80 iscontrolled by a flapper valve 84 actuated by a lever 86 which is forceloaded by a governor spring 88 in response to movement of power requestlever 42 and opposing governor centrifugal weight 92 driven by gear andshafting 40 in response to engine speed N. In this manner, the airpressure Py intermediate restriction 82 and valve 84 to which thebellows 74 is responsive is caused to vary as a function of the errorbetween a requested engine speed and actual engine speed, N. A conduit94 containing a fixed area restriction 96 communicates conduit 44 atcompressor discharge air pressure P with the relatively low pressuredrain source P The effective flow area of the discharge end of passage94 is controlled by a flapper valve 98 actuated by a lever 100 which isforce loaded by a tension spring 102 connected to levers 100 and 86. Thelever 100 is provided with spaced apart abutments 104 and 106 adapted toengage lever 86 thereby providing for a predetermined degree of movementof lever 100 relative to lever 86.

Referring to FIGS. 2 and 3, the bleed valve actuator 50 includes acasing 108 having a port 110 connected via a passage 112 to conduit 80of fuel control 38 at pressure Py, a port 114 connected via a passage116 and passage 44 to compressor discharge air at pressure P a port 118connected via a passage 120 to a source 122 of regulated air pressure PThe source 122 preferably includes a conventional fluid pressureregulator, not shown, adapted to receive compressor discharge air atpressure P via a passage 124 and passage 116 and control the flow ofsame to maintain the flow of air to port 118 at predetermined constantpressure P Ports 126 and 128 of casing 108 communicate the interior ofcasing 108 with atmospheric air pressure P,,. A passage 130 connectingport 118 with a chamber 132 vented to atmospheric pressure P via a port128 is provided with a fixed area restriction 134 and an outlet orifice136. The effective flow area of the outlet orifice 136 is controlled bya flapper valve 138 mounted on a lever 140 thereby generating a variablecontrol pressure P intermediate orifice 136 and restriction 134. Adiaphragm 142 separates two chambers 144 and 146 which are vented topassage 130 at pressure P and port 126 at atmospheric pressure Prespectively. A compression spring 148 interposed between casing 108 anddiaphragm 142 acts in opposition to the force derived from the pressuredifferential P -P acting on the exposed area of diaphragm 142. A rod 150fixedly secured to one end to diaphragm 142 extends therefrom intosliding engagement with an opening 152 in casing 108 through which rod150 extends into engagement with linkage 48. A stop member 154 suitablysecured to diaphragm 142 is adapted to engage casing 108 to limitmovement of diaphragm 142 under the influence of pressure P The leverextends through a circular opening 156 in casing 108 and is providedwith a circulasr midportion 158 pivotally secured to casing 108 by a pin160. An annular resilient seal such as O-ring 161 is suitably secured inthe wall of opening 156 to provide a fluid seal against leakage throughopening 156. The lever 140 extends into a chamber 162 and is providedwith a slotted end 164 adapted to receive one end of a stem 166 and anarm 168 pivotally secured in spaced apart relationship to lever 140 bypins 170 and 172, respectively. The arm 168 is integral with an end cap174 secured to one end of an evacuated bellows 176. The opposite end ofevacuated bellows 176 is sealed by an end cap 178 having an integral arm180 to which one end of a rod 182 is pivotally secured. The opposite endof rod 182 is fixed to one end of an arm 184 by a pin 186. The oppositeend of arm 184 is fixed by a pin 188 to a shaft 190 rotatably mounted inan opening 192 in casing 108 and extending therethrough. A resilientseal such as O-ring 194 suitably secured in the wall of opening 192provides a fluid seal against leakage through opening 192. A lever 196is fixed at one end by a pin 198 to one end of shaft 190. The oppositeend of lever 196 is provided with a follower member 198 slidably trappedbetween spaced apart annular shoulders 200 and 202 formed on rod 150.

A diaphragm 204 separates chamber 162 at pressure Py from a chamber 206vented to port 114 at pressure P and is responsive to the pressuredifferential PC Py. The stem 166 is fixedly secured at one end to thediaphragm 204 by backing plates 208 and 210.

Reference may be made to the heretofore mentioned U.S. Pat. No.3,526,091 for specific details of operation of the fuel control 38.However, for the present discussion it will be sufficient to recognizethat the engine 20 is accelerated as a result of levers 86 and 100 beingunbalanced in a direction to close flapper valves 84 and 98,respectively. The pressures P and Py increase accordingly to pressure Pthereby reducing the pressure differential P P across governor bellowsand pressurizing acceleration bellows 76 which, in turn, results inmetering valve 64 moving in an opening direction as a function ofcompressor discharge pressure P to increase fuel flow and cause theengine to accelerate accordingly.

As the engine approaches the selected engine speed corresponding to theposition of lever 42, the spring 88 is overcome by weights 92 causinglever 86 to move thereby opening flapper valve 84, which, in turn,causes a reduction in pressure Py allowing governor bellows 74 to expandin response to the increased P -P differential thereacross therebyurging metering valve 64 in a closing direction to reduce fuel flowcausing the engine to accelerate at a reduced rate and stabilize at theselected speed. FIG. 5 illustrates the relationship of the ratio ofpressures P and P to engine speed N wherein line a represents engineacceleration, point 12 is a governor break, line 0 is a governor droopand point d is a selected engine speed of 100 percent. An accelerationto a lower selected speed g is similarly executed as indicated bygovernor break point e and droop f. It will be noted that the ratioPy/PC decreases from a value of 1.0 to some typical value such asapproximately 0.85 designated by line It in the case of an accelerationto either selected speed. The decrease in Py/P occurs only as the engineaccelerates along the governor droop line c or f between points b, d ore, g, respectively, to the respective selected speed d or g therebyrendering the pressure ratio Py/Pc ideally suited as an input signal tobleed valve actuator 50 for controlling the bleed valve 46 as will bedescribed.

The bleed valve 46 is actuated by diaphragm 142 in response to thepressure differential P P imposed on diaphragm 142. The pressure P fromwhich P is derived is regulated to a fixed value above atmosphericpressure P thereby compensating for the effect of pressure P variations.The compression spring 148 is selected to provide a force which isbalanced by a pressure differential P -P acting on the exposed diaphragm142 when the differential P P is equal to one half the pressuredifferential P -P The flapper valve 138 in combination with restriction134 provides a control over pressure I which is equal to pressure P whenvalve 138 is closed and proportional to pressure P depending upon theeffective area of open valve 138. The position of lever 140 and thusflapper valve 138 is determined by the opposing forces imposed thereonby diaphragm 204 and evacuated bellows 176 which forces are derived fromthe pressure differential P P acting across the effective area, A ofdiaphragm 204 and the pressure Py acting on the effective area, A ofbellows 176 exposed thereto. For the purpose of the present discussion,it will be assumed that the forces derived from diaphragm 204 andbellows 176 are applied to lever 140 at lever arms of0.750 and 0.589,respectively, from the pivot axis of lever 140 as indicated in FIG. 2.In such a case the force balance relationship of lever 140 may bedefined by:

l. AD (PC-FY) AB Py Sin 0 wherein 0 represents the beblows 176 swingangle between the longitudinal axis of lever 140 and longitudinal axisof bellows 176.

Equation 1 may be rewritten as:

2. Py/P l/] 1.273 (A /A sin 6 wherein it will be noted that the pressureratio Py/P at which lever 140 is balanced is dependent upon the variable0.

By suitable selection of the length of lever 196 and area ratio A /A thebleed valve 46 may be made to start closing at a predetermined pressureratio Py/P and fully close at a second predetermined ratio Py/P To thatend, it will be assumed that the effective length of lever 196 and arearatio A /A are 1.75 inches and 0.1235 inch, respectively, such that thebleed valve is fully open above a pressure ratio Py/P of approximately090. In the range from 0.90 to 0.95 the bleed valve occupies a partiallyopen position in proportion to the ratio Py/P thereby avoiding abruptclosing of the bleed valve 46 which abrupt closing has an undesirabletendency to induce compressor surge.

An acceleration of the engine is initiated by an increase in pressure Pyto pressure P in the fuel control 38 in the heretofore mentioned manner.The resulting zero pressure differential across diaphragm 204 allowslever 140 to move in a direction to open valve 138 in response to thepressure P acting against bellows 176. The resulting decrease inpressure P permits spring 148 to bias diaphragm 204 into engagement witha suitablestop such as casing 108 thereby driving bleed valve 46 to openposition. The lever 196 follows diaphragm 204 causing bellows 176 topivot on pin 172 thereby reducing angle 0 in response to which the bleedvalve 46 remains open as the engine accelerates. Upon reaching governorbreak point b, the pressure Py begins to decrease from P as a result ofthe governor action of the fuel control 38 in the heretofore mentionedmanner whereupon a PC Py pressure differential is generated acrossdiaphragm 204 with the resulting force imposed on lever 140 inopposition to the force derived from pressure Py acting against bellowsI76. Upon reaching the aforementioned predetermined pressure ratio Py/Pof .95, the lever 140 becomes unbalanced in a direction to close valvecausing a corresponding rise in pressure P and movement of diaphragm 142against spring 148 which, in turn, causes bleed valve 46 to close inproportion to the decreasing ratio of pressures Py/P At theaforementioned predetermined pressure ratio of 0.90, the diaphragm 142has moved to the extent that bleed valve 46 is closed and stop member1154 is engaged with casing 103. As the bellows 176 swing angle 0increases in response to movement of diaphragm 142 and thus lever 196,the force component of bellows 176 opposing diaphragm 142 increasesaccordingly thereby tending to balance lever 140. In genera], the angle6 varies from approximately 20 to 45. The bleed valve 46 remains closed.as the engine contin ues accelerating along the governor droop line c tothe selected speed point d. The above-mentioned control of bleed valve46 in response to the decreasing pressure ratio Py/P is represented byFIG. 4. It will be noted that the bleed valve 46 is fully open only inthe Py/P pressure ratio range of 0.95 to 1.0.

Referring to FIG. 6, there is shown the structure of FIG. 2 modified foruse in controlling a conventional compressor inlet flow fence, as shownin FIG. 1. As shown 47 the output rod 150 is suitably connected toactuate the flow fence. The chambers 162 and 206 are vented toatmospheric air pressure P and compressor discharge air pressure Prespectively, thereby subjecting the diaphragm 204 to the air pressuredifferential P P,, and bellows 176 to atmospheric air pressure P,,. Itwill be noted that the position of output rod 150 is designated byarrows indicating closed and open which closed and open positionscorrespond to minimum and maximum areas, respectively, of the compressorinlet area established by the flow fence,

It will be assumed that the engine 20 is stable in operation at arelatively low engine speed as, for example, engine idle. An engineacceleration to maximum or 100 percent engine speed is initiated in theheretofore men tioned manner with regard to FIG. 2. At engine idle, thelever is balanced by the force derived from P P acting across diaphragm204 and opposing force derived from P acting against bellows 176 whichre sults in valve 138 occupying an open position whereby pressure P isreduced permitting spring 148 to actuate diaphragm against casing 108which corresponds to a closed position of the flow fence.

As the engine accelerates, compressor discharge air pressure P increasesresulting in an increase in compressor pressure ratio P /P as :afunction of engine speed as indicated in FIG. 7. Upon reaching a firstpredetermined pressure ratio P /P of 5, for example, and an engine speedcorresponding thereto, the force derived from pressure differential Py-Pacting across diaphragm 204 overcomes the opposing force component ofbellows 176 which occupies a predetermined angular position, 6, ofapproximately 68 relative to lever 140. The resulting unbalance effecton lever 140 moves valve 138 in a closing direction resulting in anincrease in pressure P and movement of diaphragm 142 against spring 148thereby actuating the flow fence, not shown, connected thereto in anopening direction to increase the effective inlet flow area ofcompressor 24. The movement of diaphragm 142 is transmitted via rod 150to lever 196 which swings bellows 176 thereby increasing the angle 6which, in turn, increases the force component of bellows 176 opposingdiaphragm 204 thereby tending to generate a force balance on lever 140.In this manner, the movement of diaphragm 142 and thus flow fenceconnected thereto is made proportional to the increasing pressure ratioP /P Upon reaching a second pressure ratio P /P of 6, for example,corresponding to a higher engine speed, the diaphragm 142 has moved to aposition where the flow fence is fully open to maximize the effectiveinlet area of compressor 24 and bellows 176 is positioned at an angle ofapproximately 80. The stop 154 engages casing 108 to prevent furthermovement of the diaphragm 142 as the engine 20 continues to accelerateto the selected maximum speed.

An engine deceleration from the maximum speed to the idle speed resultsin reversal of the abovementioned operation. It will be understood thatthe flow fence is fully closed in the engine speed operating range belowthe above-mentioned first predetermined pressure ratio P /P of and fullyopen in the engine speed operating range above the above-mentionedsecond predetermined pressure ratio P /P of 6. In the speed rangebetween the first and second predetermined pressure ratio P /P of 5 and6, the diaphragm 142 and thus flow fence is positioned intermediate theopen and closed position in proportion to the pressure ratio P /P Theabove-mentioned specific values assigned to the various lever arms andarea ratio of diaphragm 204 and bellows 176 are representative only andmay be suitably changed to vary the relationship between movement ofbleed valve 46 and pressure ratio Py/P or flow fence position andpressure ratio P /P depending upon the characteristics of a given engineas will be recognized by those persons skilled in the art.

We claim:

1. Control apparatus for a gas turbine engine having a variable geometryair compressor comprising:

a fluid pressure responsive output member operatively connected to saidair compressor for varying the geometry thereof;

valve means for controlling the fluid pressure to which said pressureresponsive member responds;

control means responsive to first and second air pressures at least oneof which varies in a predetermined manner in response to engine speed,said control means having a lever member operatively connected to saidvalve means for actuating the same in proportion to the ratio of saidfirst and second air pressures over a predetermined range of enginespeeds during an acceleration of the engine to a selected speed;

said control means having a first air pressure responsive memberoperatively connected to said lever member and responsive to said firstand second air pressures, and a second air pressure responsive memberoperatively connected to said lever member and responsive to said secondair pressure for loading said lever member in opposition to said firstair pressure responsive member; and means operatively connecting saidfluid pressure responsive output member and said second air pres- 5 sureresponsive member for positioning said second air pressure responsivemember in response to movement of said output member to vary theeffective force component of said second air pressure responsive memberopposing said first air pressure responsive member.

2. Control apparatus for a gas turbine engine having a variable geometryair compressor comprising:

output means operatively connected to said air compressor for varyingthe geometry thereof in response to a fluid pressure;

valve means for controlling said fluid pressure in response to anoperational condition;

control means responsive to a first air pressure and a second airpressure one of which varies as a function of engine speed for actuatingsaid valve means in proportion to the ratio of said first air pressureand said second air pressure over a predetermined range of engine speedsduring an acceleration of the engine to a selected speed;

lever means operatively connecting said control means with said valvemeans;

first pressure means responsive to said first air pressure and saidsecond air pressure for supplying said lever means with an operationalsignal;

second pressure means responsive to said second air pressure forsupplying said lever means with a loading force in opposition to saidfirst pressure means; and

linkage means for connecting said output means and said second pressuremeans for varying a component of the loading force as a function ofengine speed.

3. Control apparatus for a gas turbine engine having a variable geometryair compressor as claimed in claim 1 wherein:

said one air pressure which varies with engine speed is compressordischarge air pressure.

4. Control apparatus for a gas turbine engine having a variable geometryair compressor as claimed in claim 1, wherein:

said first air pressure is compressor discharge air pressure; and

said second air pressure is derived from compressor discharge airpressure and modified by engine speed responsive means over saidpreetermined range of engine speeds.

5. Control apparatus for a gas turbine engine having a variable geometryair compressor as claimed in claim 1, wherein:

said first air pressure responsive member is a diaphragm exposed to saidfirst and second air pressures and responsive to the differentialtherebetween;

said second air pressure responsive member is an evacuated bellowspivotally mounted at one end to said lever member and at its oppositeend to said output member;

said evacuated bellows being actuated angularly relative to said levermember by said output member to vary the effective force componentthereof directed against said lever member in opposition to saiddiaphragm.

6. Control apparatus for a gas turbine engine having a variable geometryair compressor as claimed in claim 1, wherein:

said variable geometry is defined by a compressor air bleed valve, saidcontrol apparatus further includengine governor means having acharacteristic governor droop range of operation for controlling engineoperation;

said control means operatively connected to said compressor bleed valvefor actuating the same to an open position in response to a firstpredetermined ratio of said first and second air pressures during anacceleration of said engine to a selected speed;

said control means actuating said bleed valve to close the sameproportionally with a decrease in said ratio of said first and secondair pressures over a predetermined range of engine speed within saidgovernor droop range of operation 7. Control apparatus for a gas turbineengine having a variable geometry air compressor as claimed in claim 6,wherein:

said second air pressure is controlled by said governor means inresponse to engine speed.

8. Control apparatus for a gas turbine engine having a variable geometryair compressor as claimed in claim 5, wherein:

said diaphragm and bellows have a predetermined fixed area ratio.

9. Control apparatus for a gas turbine engine having a variable geometryair compressor as claimed in claim 1, wherein:

said first and second air pressures are upon closure of a flapper valvemeans equalized to establish said first predetermined ratio.

10. Control apparatus for a gas turbine engine having a variablegeometry air compressor as claimed in claim iii 1, wherein:

said second air pressure responsive member is an evacuated bellowspivotally connected at one end to said lever means and at the oppositeend to a swinging arm adapted to swing said bellows about said pivotconnection with said lever member; and

lever means operatively connected to said output member and saidswinging arm for actuating said arm in response to movement of saidoutput member. 11. Control apparatus for a gas turbine engine having avariable geometry air compressor as claimed in claim 1, wherein saidvariable geometry is defined by a compressor inlet flow fence andwherein:

said fluid pressure responsive output member is operatively connected tosaid flow fence for actuating the same; said first and second airpressures are atmospheric and compressor discharge air pressures,respectively. 12. Control apparatus for a gas tubine engine having avariable geometry air compressor as claimed in claim 11, wherein:

said inlet flow fence is operatively connected to said fluid pressureresponse output member by a linkage means, said inlet flow fence isactuated to a fully closed position in response to a said ratio of firstand second air pressures below a first predetermined ratio thereof and afully open position in response to said ratio of first and second airpressures above a second predetermined ratio thereof;

said inlet flow fence is actuated in an opening direction in proportionto said ratio of first and second air pressures as said ratio increasesfrom said first to said second predetermined ratio.

=l l i =l=

1. Control apparatus for a gas turbine engine having a variable geometryair compressor comprising: a fluid pressure responsive output memberoperatively connected to said air compressor for varying the geometrythereof; valve means for controlling the fluid pressure to which saidpressure responsive member responds; control means responsive to firstand second air pressures at least one of which varies in a predeterminedmanner in response to engine speed, said control means having a levermember operatively connected to said valve means for actuating the samein proportion to the ratio of said first and second air pressures over apredetermined range of engine speeds during an acceleration of theengine to a selected speed; said control means having a first airpressure responsive member operatively connected to said lever memberand responsive to said first and second air pressures, and a second airpressure responsive member operatively connected to said lever memberand responsive to said second air pressure for loading said lever memberin opposition to said first air pressure responsive member; and meansoperatively connecting said fluid pressure responsive output member andsaid second air pressure responsive member for positioning said secondair pressure responsive member in response to movement of said outputmember to vary the effective force component of said second air pressureresponsive member opposing said first air pressure responsive member. 2.Control apparatus for a gas turbine engine having a variable geometryair compressor comprising: output means operatively connected to saidair compressor for varying the geometry thereof in response to a fluidpressure; valve means for controlling said fluid pressure in response toan operational condition; control means responsive to a first airpressure and a second air pressure one of which varies as a function ofengine speed for actuating said valve means in proportion To the ratioof said first air pressure and said second air pressure over apredetermined range of engine speeds during an acceleration of theengine to a selected speed; lever means operatively connecting saidcontrol means with said valve means; first pressure means responsive tosaid first air pressure and said second air pressure for supplying saidlever means with an operational signal; second pressure means responsiveto said second air pressure for supplying said lever means with aloading force in opposition to said first pressure means; and linkagemeans for connecting said output means and said second pressure meansfor varying a component of the loading force as a function of enginespeed.
 3. Control apparatus for a gas turbine engine having a variablegeometry air compressor as claimed in claim 1 wherein: said one airpressure which varies with engine speed is compressor discharge airpressure.
 4. Control apparatus for a gas turbine engine having avariable geometry air compressor as claimed in claim 1, wherein: saidfirst air pressure is compressor discharge air pressure; and said secondair pressure is derived from compressor discharge air pressure andmodified by engine speed responsive means over said preetermined rangeof engine speeds.
 5. Control apparatus for a gas turbine engine having avariable geometry air compressor as claimed in claim 1, wherein: saidfirst air pressure responsive member is a diaphragm exposed to saidfirst and second air pressures and responsive to the differentialtherebetween; said second air pressure responsive member is an evacuatedbellows pivotally mounted at one end to said lever member and at itsopposite end to said output member; said evacuated bellows beingactuated angularly relative to said lever member by said output memberto vary the effective force component thereof directed against saidlever member in opposition to said diaphragm.
 6. Control apparatus for agas turbine engine having a variable geometry air compressor as claimedin claim 1, wherein: said variable geometry is defined by a compressorair bleed valve, said control apparatus further including; enginegovernor means having a characteristic governor droop range of operationfor controlling engine operation; said control means operativelyconnected to said compressor bleed valve for actuating the same to anopen position in response to a first predetermined ratio of said firstand second air pressures during an acceleration of said engine to aselected speed; said control means actuating said bleed valve to closethe same proportionally with a decrease in said ratio of said first andsecond air pressures over a predetermined range of engine speed withinsaid governor droop range of operation
 7. Control apparatus for a gasturbine engine having a variable geometry air compressor as claimed inclaim 6, wherein: said second air pressure is controlled by saidgovernor means in response to engine speed.
 8. Control apparatus for agas turbine engine having a variable geometry air compressor as claimedin claim 5, wherein: said diaphragm and bellows have a predeterminedfixed area ratio.
 9. Control apparatus for a gas turbine engine having avariable geometry air compressor as claimed in claim 1, wherein: saidfirst and second air pressures are upon closure of a flapper valve meansequalized to establish said first predetermined ratio.
 10. Controlapparatus for a gas turbine engine having a variable geometry aircompressor as claimed in claim 1, wherein: said second air pressureresponsive member is an evacuated bellows pivotally connected at one endto said lever means and at the opposite end to a swinging arm adapted toswing said bellows about said pivot connection with said lever member;and lever means operatively connected to said output member and saidswinging arm for actuating said arm in response to movement of saidoutput member.
 11. Control apparatus for a gas turbine engine having avariable geometry air compressor as claimed in claim 1, wherein saidvariable geometry is defined by a compressor inlet flow fence andwherein: said fluid pressure responsive output member is operativelyconnected to said flow fence for actuating the same; said first andsecond air pressures are atmospheric and compressor discharge airpressures, respectively.
 12. Control apparatus for a gas tubine enginehaving a variable geometry air compressor as claimed in claim 11,wherein: said inlet flow fence is operatively connected to said fluidpressure response output member by a linkage means, said inlet flowfence is actuated to a fully closed position in response to a said ratioof first and second air pressures below a first predetermined ratiothereof and a fully open position in response to said ratio of first andsecond air pressures above a second predetermined ratio thereof; saidinlet flow fence is actuated in an opening direction in proportion tosaid ratio of first and second air pressures as said ratio increasesfrom said first to said second predetermined ratio.